Instability wave-streak interactions in a hypersonic boundary layer at flight conditions

Area of Science:

• Aerospace Engineering
• Fluid Dynamics
• Hypersonics

Background:

• Hypersonic boundary layers are susceptible to instabilities that trigger transition to turbulence.
• Understanding transition mechanisms is crucial for predicting aerodynamic performance and thermal loads.

Purpose of the Study:

• To investigate the interaction between stationary streaks and instability waves in hypersonic boundary layers.
• To analyze the nonlinear evolution of disturbances and their effect on laminar-turbulent transition.
• To assess the stabilizing influence of streaks on flow instabilities.

Main Methods:

• Numerical computations, including direct numerical simulations (DNS) and parabolized stability equations (PSE).
• Analysis of modal instability characteristics using planar eigenvalue analysis.
• Simulations matched conditions from the HIFiRE-1 flight experiment (Mach 5.30 cone).

Main Results:

• Stationary streaks reduce the amplification of instability waves, potentially delaying transition onset.
• The spanwise varying component of streaks significantly impacts Mack-mode instability amplification.
• A specific streak wavenumber (1.4x optimal) proved most effective in stabilizing Mack-mode instabilities.

Conclusions:

• Stationary streaks offer a significant stabilization effect on hypersonic boundary layers, delaying transition.
• Transition onset is delayed until streak amplitudes reach ~35% of freestream velocity, after which streak instabilities dominate.
• A potential transition delay exceeding 100% of the natural laminar region length is achievable.